The present invention relates to a refrigeration cycle, and more particularly to a refrigeration cycle connecting a compressor, a condenser, an expansion device, and an evaporator in a loop by piping, using a mixed refrigerant or alternative refrigerant mixing at least one or two or more types of hydrochlorofluorocarbon refrigerants.
The compressor used in the refrigeration cycle, in particular, is the maintenance-free enclosed compressor composed as disclosed in Japanese Laid-open Patent 62-298680, a compressive mechanism filling an enclosed container with a mixed refrigerant and oil for compressing by sucking refrigerant, an oil pump for feeding the oil into machine sliding parts, and a motor for driving them by drive shaft.
On the other hand, the refrigeration cycle uses a refrigerant such as chlorofluorocarbons (CFCs) or R12 and designated hydrochlorofluorocarbons (HCFCs) or R22. The specific CFCs are chemically stable, and free from flammability and toxicity as compared with hitherto known refrigerants such as sulfur dioxide and methyl chloride, and are widely applied as ideal refrigerants and have been used for many years.
Recently, however, chlorine atoms contained in the molecules of specific CFCs are recognized to induce destruction of the ozone layer, and development and use of alternative refrigerants not containing chorine atoms have been attempted.
As a practical alternative refrigerant, for example, a chlorine-free refrigerant such as hydrofluorocarbon has been proposed (Hydraulic and Pneumatic Technology, June 1994, Nippon Kogyo Shuppan). As an alternative refrigerant, for example, R134a is used.
Since chlorine is not contained in the refrigerant, however, the alternative refrigerant is not expected to have an excellent lubricity as in the conventional specific CFCs. Accordingly, as the oil to be contained in the enclosed container, an oil compatible with the alternative refrigerant is particularly required. The oil contained in the enclosed container is stirred by the alternative refrigerant discharged from the compressive mechanism into the enclosed container, and is further stirred by rotor of the motor. At this time, if the oil is compatible with the alternative refrigerant, the oil is stirred well with the refrigerant discharged into the enclosed container, and permeates into narrow gaps in the sliding parts of the machines. Therefore, together with the effects of the supply of oil by an oil pump, the lubricating performance is enhanced. As such oil, as disclosed in Japanese Laid-open Patent 6-235570, an ester derivative synthetic oil is used.
However, when an enclosed compressor is operated in such conditions and the refrigeration cycle is executed and continued, foreign matter may be deposited in the inlet and outlet of capillary tubes forming the expansion device, and the flow of the refrigerant is blocked relatively early, and the refrigerating function is lowered.
To elucidate and study the cause of such a defect, various experiments were conducted. As a result, it was found to be due to the use of the ester oil as the oil compatible with the alternative refrigerant. If moisture invades when enclosing the refrigerant piping, or moisture is formed after enclosing due to some reason, the ester oil is hydrolyzed by the moisture, and produces fatty acid. The fatty acid corrodes the parts in the piping, forms metal soap and produces sludge. The ester oil is low in stability, and therefore foreign matter is likely to be dissolved and mixed in when the temperature is raised, or foreign matter is likely to precipitate when the temperature is lowered. At the inlet of the capillary tube, the flow velocity of the refrigerant drops, and hence, the precipitating foreign matter is likely to be adhered to cause clogging. At the outlet of the capillary tube, since the temperature is lowered, foreign matter is likely to precipitate and stick.
The above Japanese Laid-open Patent 6-235570 discloses a refrigeration cycle characterized by solving the problems of faulty flow of refrigerant or clogging in the capillary tube, by capturing the foreign matter by installing a filter immediately at the upstream side in the flow direction of the refrigerant in the capillary tube in the midst of the refrigerant piping.
However, the above filter structure is complicated and expensive, and it cannot cope with the defect of precipitation due to temperature drop at the outlet of the capillary tube and immediate deposit of the precipitates. In the refrigeration cycle operated by the heat pump, if the flow direction of refrigerant is reverse in changeover of heating and cooling, the filter must be provided at both sides of the capillary tube, which further adds to the cost.
It is an object of the invention to present a refrigeration cycle of high reliability capable of suppressing deposit of foreign matter at the outlet or inlet of the capillary tube in a simple and inexpensive structure, regardless of the changeover from a cooling operation to a heating operation, and vice versa.